A method is known of measuring objects mechanically in the conventional way and also of measuring them optically, e.g. by taking 3-D photographs. With this method, in order to spatially determine the object, the light section method and the stereo recording method are known, amongst others. Measurements taken using optic apparatus of this kind is problematic because the object to be measured must be sufficiently optically accessible, i.e. the surfaces which are to be measured must be directly visible.
However, a number of instances arise where access to the object to be measured is so poor that direct visibility of the object, at least from the angle of view required for the measurement to be taken, is not possible. This is most frequently the case due to the spatial limitations for the measuring apparatus, and so in other words the space around the object to be measured is so small that neither the measuring apparatus nor a sufficiently large optical instrument with deflector mirrors and the like for taking the measurements is able to be placed in position or accommodated.
Such an example is in dentistry where a set of teeth has to be measured for jaw-orthopaedic purposes, e.g. if gaps between teeth have to be corrected by the use of the "Edge-Wise-Wire Spring-Technique". With this technique, clamping elements (known as brackets) are fixed to the teeth to which elements a wire spring is fixed. This is shaped in such a way that it applies the necessary forces and moments to the teeth for correction in the necessary way. To adjust the correct forces and moments, the wire spring has to be correctly set, and a specially made wire spring has to be made for each individual patient when that patient is treated. In this respect, a proposal has already been made to use computer controlled bending machines to produce the correctly shaped wire springs. To this end, at least the spatial coordinates of the bracket must be accurately known. Also, it would be helpful if the person treating the patient were to have exact data relating to the chewing surfaces, for the aim of correcting the teeth is to produce positioning of the teeth where the chewing surfaces of the corresponding teeth of the upper and lower jaw are correct relative to each other.